As a parent, do I have the right to check my teenager's phone?

Have two sons, 13 and 16. Yesterday more joking than serious I asked to see my eldest's phone and he equally jokingly declined. I insisted and in the end things turned serious, with him insisting not to give it, and mentioning he has a right to privacy.So i got thinking, who's right here? He has paid the phone with his own money, if that matters, and I am paying his usage bill. I don't suspect him of anything, and wanted mostly to play around rather than go to snapchat/instagram/whatsap/facebook and start reading his messages (which would take me a couple of days honestly).What does the sub think?Thanks via /r/Parenting https://ift.tt/2ViXINW